Conventionally, in a pneumatic tire for heavy load, in order to suppress uneven wear of a shoulder rib, a method has been widely used in which a thin rib-shaped uneven abrasion sacrificing part (hereinafter abbreviated as BCR) having a step in a clearance thereof from the surface of a tread is formed in a circumferential main groove, and in which the BCR generates shearing force in the opposite direction to the traveling direction of a vehicle to reduce shearing force working on an edge portion of the shoulder rib body in the traveling direction (see Patent Document 1).
FIG. 6(a) illustrates a partial plan exploded view of a tread of a pneumatic tire for heavy load having BCRs. Meanwhile, FIG. 6(b) illustrates a cross-sectional view of the pneumatic tire for heavy load illustrated in FIG. 6(a) as taken in the A-A′ direction.
As illustrated in FIGS. 6(a) and 6(b), a tread TR10 includes linear circumferential grooves 131 provided thereon at opposite sides of a tire equator line CL, and center ribs 112 are provided at the outer sides of the respective circumferential grooves 131. Further, linear circumferential grooves 132 are provided at the outer sides of the center ribs 112. Each of the circumferential grooves 132 includes a BCR 121 formed therein, and the BCR 121 has a step in a clearance thereof from the surface of the tread TR10. Furthermore, shoulder ribs 111 are provided at the outer sides of the circumferential grooves 132.
In the conventional pneumatic tire for heavy load as illustrated in FIG. 6, the shearing force (shearing distortion) working in the opposite direction to the traveling direction of a vehicle is generated due to the step region formed by the BCR 121 and the circumferential groove 132.
Further, although not illustrated, Patent Documents 2 and 3 report that the BCR is also provided in a circumferential main groove which is positioned on the equator line of the tread and extends in the circumferential direction, and that the uneven wear resistance performance is improved by the BCR.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2-88311 (the scope of claims, etc.)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2000-23508 2000-238508 (the scope of claims, etc.)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-254905 (the scope of claims, etc.)